The present invention relates generally to the field of surface coverings. More particularly, the present invention relates to a self-adhering surface covering having a pressure-sensitive adhesive layer and a barrier layer to substantially prevent undesired or premature bonding to a surface and a method of making the same.
Self-adhering surface coverings, such as self-adhering floor tiles, have been commercially available for several decades. Typically, such self-adhering surface coverings are packaged in cardboard cartons with 20-50 tiles per carton and have a shipping weight of approximately 10-65 pounds. Commonly, the self-adhering surface coverings consist of a filled polyvinyl chloride substrate having a pressure-sensitive adhesive layer which is covered by a release layer, such as a silicone treated paper. The release layer prevents adherence of the surface covering units to one another when positioned together in the stack. To install such a product, an installer simply peals the release layer from the adhesive layer, places the self-adhering surface covering at a desired site of bonding, and presses the surface covering to adhere the adhesive layer to the surface of the bonding site. Self-adhering surface coverings allow the installer to eliminate a time consuming and often times messy adhesive spreading step. However, the release paper adds to the cost of the product and has the disadvantage of requiring the installer to collect the discarded release paper and provide proper disposal thereof. This disadvantage ranges from an inconvenience on small installation projects to a significant disposal problem on large projects. Regardless of the job size, disposal of the release paper provides an environmental burden in that it is generally not recyclable and often requires its disposal in limited land-fill space.
There are many references describing surface coverings having adhesive layers. For example, U.S. Pat. Nos. 3,331,729 and 3,413,168, both to Danielson et al. describe that a large pressure sensitive adhesive tape or sheet can be made repositionable by partially embedding into the adhesive layer a large number of tiny hollow microspheres, there called xe2x80x9cmicroballoonsxe2x80x9d. The Danielson tape is made by randomly attracting microballoons to a polyethylene-coated paper liner, partially pressing the microballoons into the polyethylene while it is being softened by heat, applying a pressure-sensitive adhesive over the microballoons, and covering the exposed surface of the adhesive with a decorative film. Then after stripping off a paper liner, the protruding microballoons permit the adhesive-bearing decorative film to be slid along the surface of a substrate until it is precisely positioned, whereupon hand pressure is applied to crush the microballoons, thus allowing the adhesive to contact and to become bonded to the substrate.
Large-scale manufacture of the Danielson article requires considerable skill to ensure that the microballoons are uniformly distributed in order to keep every part of the pressure-sensitive adhesive layer from contacting and sticking prematurely to the substrate. Manufacture also requires a special release liner into which the microballoons can be partially embedded.
U.S. Pat. No. 3,314,838 to Erwin describes a repositionable pressure-sensitive adhesive sheet which is similar to those of the Danielson patents except being made by dispersing microballoons into a spreadable liquid from which the pressure-sensitive adhesive is to be coated. The microballoons xe2x80x9cshow a tendency to appear at the exposed surfacexe2x80x9d of the resulting pressure-sensitive adhesive layer, thus giving it a pebbled surface that is said to make the sheet repositionable until the microballoons are crushed (col. 2, lines 56-68).
U.S. Pat. No. 4,376,151 to Parrotta shows a pressure-sensitive adhesive sheet which, like that of Erwin, has hollow microspheres or microballoons at the surface of its pressure-sensitive adhesive layer, but its adhesive has substantially no adhesive tack except upon application of a threshold pressure. The Parrotta sheet is said to differ from that of Erwin because the latter is activated by very low pressure and is somewhat tacky to the fingers.
U.S. Pat. No. 3,301,741 to Henrickson et al. makes a pressure-sensitive adhesive sheet repositionable by shaping its surface into a pebbly contour of small protrusions that are covered by non-adhesive, continuous, fragile protective caps. Those caps had been formed by embossing polyethylene-coated paper to form a uniform array of depressions, filling the depressions with non-adhesive material such as a solution of polymethylmethacrylate, and wiping the solution off the areas between the depressions. After the sheet has been positioned, pressure is applied, shattering the caps and causing the adhesive to flow around the fragments into intimate contact with a substrate to which the sheet is being applied.
U.S. Pat. No. 4,556,595 to Ochi makes a pressure-sensitive adhesive sheet repositionable by the random application of tiny solid particles over the adhesive surface. After the sheet has been positioned over a substrate, pressure is applied to force the particles into the adhesive, thus allowing the adhesive to contact and become bonded to the substrate. The Ochi patent preferably employs a xe2x80x9crelease paper in order to prevent intrusion and dispersion of the non-adhesive solid particles in the adhesive which may occur by application of some pressure during storagexe2x80x9d (col. 9, lines 2-7). However, it does not explain how that release paper can prevent the particles from being pushed into the adhesive layer to destroy their utility.
In U.S. Pat. No. 3,554,835 to Morgan, the face of a pressure-sensitive adhesive sheet is provided with dots of release material that permit the sheet to be slid over a substrate until pressure is applied to force the adhesive into contact with the substrate.
In U.S. Pat. No. 4,054,697 to Reed et al., the face of a pressure sensitive adhesive sheet is provided with a coating of a discontinuous layer of resilient, non-adhesive, solid particles that permit repositioning on a substrate until the particles are deformed under pressure to such an extent as to bring the adhesive and the substrate into filler contact.
Common to the background discussed above is that the particles are used to make a pressure-sensitive adhesive surface coverings repositionable and do not address the problem of preventing adherence to adjacent surfaces during storage under loads and potentially high temperatures. Hence, if sufficient particles have been employed to ensure that every portion of the pressure-sensitive adhesive layer is safely kept out of contact with the substrate to which it is being applied, the particles may have such high density as to interfere with the bonding strength. In other words, if high bonding strength is required, it may be necessary to reduce the amount of particles even though some pieces of the pressure sensitive adhesive sheet might become prematurely bonded to a substrate and thus need to be destroyed. Further, if the surface covering has a decorative substrate which is thin, such as a vinyl film, an additional problem can occur when pressure is applied to force its pressure-sensitive adhesive into bonding contact with a surface by the particles being forced into the adhesive layer to produce a disfiguring pimpling of the substrate.
Despite existing self-adhering surface coverings which employ particles to prevent undesired adherence to surfaces, the need remains for a self-adhering surface covering which does not employ a release layer and is inexpensively produce. Further, there remains a need for a method of manufacturing such a self-adhering surface covering. Accordingly, it is to the provision of a self-adhering surface covering that meets these needs that the present invention is primarily directed.
This invention overcomes the disadvantages of the prior art by providing a self-adhering surface covering which avoids undesired adherence of the surface covering under loads which can be experienced during shipping and storage to surfaces without employing a release layer or paper. In accordance with the present invention, the self-adhering surface covering comprises a substrate having first and second surfaces, a pressure sensitive adhesive layer disposed on the second surface of the substrate and has an adhesive surface distal from the second surface, and a barrier layer disposed on the adhesive surface. In one aspect, the self-adhering surface covering has substantially no tack at about 10 pounds/inch2 (xe2x80x9cpsixe2x80x9d) at about 140xc2x0 F. when placed in contact with the first surface of an adjacent substrate, but has tackiness when subjected to a load of about 20 psi at about 75xc2x0 F. In another aspect, the adhesive layer comprises a substantially non-stringing adhesive. Substantially non-adhesive particles comprise the barrier layer. Such particles while disposed on the adhesive layer resist crushing when subjected to a load of at least about 10 psi, yet are crushable when subjected to a load of about 20 psi or greater. Additionally, the particles have a diameter which is at least about equal to or greeter than the thickness of the adhesive layer. In one embodiment of the present invention, particles are distributed randomly and substantially uniformly over the surface of the adhesive layer. In an alternative embodiment, at least a portion of the particles is distributed over the surface of the adhesive layer in a pattern or design.
Further, in accordance with the present invention, a method of making the self-adhering surface covering comprises applying an adhesive to a substrate to form an adhesive layer having an adhesive surface, and applying a barrier layer comprising substantially non-adhesive particles to the adhesive surface to form the self-adhering surface covering. The particles, while disposed on the adhesive layer, resist crushing when subjected to a load of at least about 10 psi, but are crushable when subjected to a load of about 20 psi or greater. In one aspect of the method of the present invention, the self-adhering surface covering has substantially no tack at about 10 psi at about 140xc2x0 F. but has tack at about 20 psi at about 75xc2x0 F. In another aspect of the method of the present invention, the adhesive layer comprises a substantially non-stringing adhesive.
Thus, a unique self-adhering surface covering and a method of making the same is now provided that successfully addresses the shortcomings of existing self-adhering surface coverings and provides distinct advantages over such self-adhering surface coverings. Additional objects, features, and advantages of the invention will become more apparent upon review of he detailed description set forth below when taken in conjunction with the accompanying drawing figures, which are briefly described as follows.